Body area networks (BANs) are a subset of wireless personal area networks (WPANs), which in turn are a subset of personal area networks (PANs). Such networks can be used for communicating data between devices that are located close to one person.
BCC has been proposed as a prime candidate for the physical layer technology of BANs. It is also considered in the IEEE 802.15.6 BAN standardization.
BCC signals are conveyed over a human body instead of through the air. Therefore, a communication based on such signals is confined to an area close to the human body. This is in contrast to radio frequency (RF) communications, where a much larger area is covered.
Thus, when using BCC signals, a communication is only possible between devices situated on, connected to or placed close to the same human body. This enables the creation of a secure BAN.
A schematic diagram of a BCC system is shown in FIG. 7. A BCC system 700 comprises a transmitter 705 and a receiver 710 as well as electrodes 715, 720, 725 and 730. The transmitter 705 is connected to the electrodes 715 and 720, and the receiver 710 is connected to the electrodes 725 and 730, wherein each of the electrodes 715, 720, 725 and 730 is illustrated as a flat plate in FIG. 7. The transmitter 705 is capacitively coupled to the receiver 710 through a human body in order to transmit signals from the former to the latter. For example, they can be capacitively coupled through a person's forearm as depicted in FIG. 7. As an electrostatic coupling is used to transmit signals from the transmitter 705 to the receiver 710, a current return path is required. Such return path is provided by the air (dielectric) and earth ground (dielectric and conductor).
BAN technology may be applied in medical on-body sensor networks, where it is important that the sensors exchange data (or identification keys) only with other sensors on the same human body. Other applications of this technology can be e.g. in the fields of sports, military and security.
On the other hand, capacitive technology has also been proposed for sensing physiological signals such as e.g. electrocardiogram (ECG) signals, electroencephalogram (EEG) signals and electromyogram (EMG) signals. When using capacitive technology, the sensing can be contactless. That is, a sensor does not have to touch a person's body. This is in contrast to previously proposed sensor systems such as e.g. a usual ECG system. With these systems the sensors have to be glued or connected with gel to a person's body. As no such contact is needed when using capacitive technology, sensors may be integrated e.g. in clothing with this technology. Thus, new applications such as e.g. in the field of wellness are enabled by employing capacitive technology for sensing purposes.
A schematic diagram of a capacitive physiological sensing device is shown in FIG. 8. A capacitive physiological sensing device 800 comprises a sensor processing unit 805 as well as electrodes 810 and 815. The sensor processing unit 805 is connected to the electrodes 810 and 815. The electrodes 810 and 815 are placed close to a human body in order to pick up a signal from the same by means of a capacitive coupling. As illustrated in FIG. 8, they may be located e.g. at a person's forearm. A raw signal picked up by the electrodes 810 and 815 is input to the sensor processing unit 805, which conditions and processes this raw signal to obtain a desired physiological signal such as e.g. an ECG signal.
Physiological signals output by capacitive physiological sensing devices such as e.g. the capacitive physiological sensing device 800 shown in FIG. 8 can be transmitted over wires or via RF technology (such as e.g. ZigBee or WiFi). If the physiological signals are transmitted over wires, all capacitive physiological sensing devices have to be connected by wires. This may result in many errors during operation of a system comprising a plurality of capacitive physiological sensing devices. For example, when using such system in a clinical environment, errors may occur due to loose contacts and people moving. Further, a system of this kind does not provide a convenient sensing for lifestyle applications such as e.g. wellness and sports, due to a clutter of wires. In summary, sensing systems based on wired communications are unreliable and inconvenient.
The above mentioned problems can be solved by using RF connections or links for transmitting physiological signals. However, such RF links show the disadvantage that a human body at which sensing devices for sensing the physiological signals are located blocks the RF links. Further, the RF communication range is not limited to one person. An additional disadvantage of the RF approach consists in that an extra RF communication solution has to be added to every sensing device, which significantly increases the costs of the solution and its power consumption.
Thus, the operation of RF-based sensing systems becomes unreliable due to body blockage. Further, their operation even becomes insecure due to providing a communication range that is not limited or restricted to one person. In addition, each sensing device of such system requires an extra antenna and RF solution for the communication.
WO 2006/064397 A2 discloses a wireless network for monitoring a patient, wherein the wireless network comprises at least one wearable monitor including a physiological condition sensor coupled to the patient to sense data related to one physiological function of the patient, and a first body communication unit that interfaces with the physiological condition sensor to communicate over the patient utilizing a near field capacitive body coupled protocol. The wireless network further comprises a relay system including a second body communication unit that receives data from and communicates with the first body communication unit utilizing the near field capacitive body coupled protocol, and an external communication unit that communicates the data to a remote medical monitoring station. That is, the arrangement described in this document comprises a conventional sensor dedicated to sensing purposes and a separate body communication unit dedicated to communicating purposes.